The board is cut into dominoes. A magnet has a plus end and a minus end. The numbers at the edges tell you how many of each sign go in every row and column.
The rules
- Each domino covers 2 boxes.
- A domino is either a magnet or neutral. A magnet has one plus end and one minus end. A neutral domino has no signs.
- Two plus signs may not touch side by side. Two minus signs may not touch side by side either.
- Matching signs may touch at the corners.
- The numbers at the top and on the left count the plus signs in that column or row.
- The numbers at the bottom and on the right count the minus signs in that column or row.
- A missing number allows any count. It does not mean 0.
- When the board is checked, dominoes you left open count as neutral.
These are the classic rules. Quirk does not change them.
A worked example
This board has 2 rows and 4 columns. Boxes with the same letter form 1 domino, so every domino lies flat.
| Column 1 | Column 2 | Column 3 | Column 4 | Plus in row | Minus in row | |
|---|---|---|---|---|---|---|
| Row 1 | A | A | B | B | 1 | 1 |
| Row 2 | C | C | D | D | 2 | 2 |
| Plus in column | 1 | 1 | 0 | 1 | ||
| Minus in column | 1 | 1 | 1 | 0 |
- Row 2 needs 2 plus and 2 minus. That is 4 signs, and row 2 has only 4 boxes. So dominoes C and D are both magnets.
- Column 3 has a plus count of 0. So row 2, column 3 cannot be plus. It is minus, and row 2, column 4 is plus.
- Now look at domino B in row 1. Column 3 already has its 1 minus, and it allows no plus. So row 1, column 3 gets no sign.
- A magnet always has a sign at both ends. So domino B is neutral.
- Row 1 needs 1 plus and 1 minus. Only domino A is left, so A is a magnet.
- Row 2, column 2 sits next to the minus in column 3. Two minus signs may not touch, so it is plus. Row 2, column 1 is minus.
- Row 1, column 1 sits above that minus, so it is plus. Row 1, column 2 is minus.
- Check: row 1 is plus, minus, blank, blank. Row 2 is minus, plus, minus, plus. Every count matches, and no matching signs touch.
Beginner techniques
Look for a 0 first
A plus count of 0 means no plus in that line. A domino lying along that line must be neutral, because a magnet there adds a plus. A domino crossing the line can only put a minus in it.
Lines that need every box
Add a line's plus and minus counts. If the total equals the number of boxes, every box needs a sign. Every domino in that line is then a magnet.
Check the neighbours
Plus cannot touch plus along a side, and minus cannot touch minus. A box next to a minus can only be plus or blank.
Plus and minus take turns
In a line where every box has a sign, the signs must take turns. A column of 7 with 4 plus and 3 minus starts and ends with plus.
Count what a line can hold
A magnet lying along a line adds 1 plus and 1 minus to it. An upright magnet adds just 1 sign to each row it covers. Count what each line can still take.
Common mistakes
- Reading a missing number as 0. A missing number allows any count.
- Mixing up the sides. Plus counts sit at the top and left. Minus counts sit at the bottom and right.
- Giving a magnet only one sign. A magnet always has a plus end and a minus end.
- Forgetting that an upright magnet puts both its signs in the same column.
- Worrying about corners. Matching signs may touch at a corner.
Questions
What does neutral mean?
A neutral domino has no plus and no minus. It does not count for any row or column.
Does a missing number mean 0?
No. A missing number means that line can have any count of that sign.
Do I have to mark every neutral domino?
No. When the board is checked, any domino you left open counts as neutral. Marking them can still help you keep track.
What sizes are there?
Boards go from 4 by 4 up to 8 by 8. Bigger boards ask you to count across more lines at once.
Does every puzzle have one answer?
Yes. Each board in Quirk has exactly one answer, and you can find it without guessing.
Is it good for beginners?
Yes. The first lesson shows a single domino in all its states. Later lessons add one idea at a time.
Related puzzles
Playing it in Quirk
Tap one end of a domino to put plus there. The other end gets minus. Tap again to turn the magnet round, again for neutral, and once more to clear it.
Drag across several dominoes to give them all the same mark as the first one. If you get stuck, a hint shows the next step and why. You can undo a move or start again.
